1. Field of the Invention
This relates to a magnetic recording/reproducing apparatus and, particularly, to a magnetic recording/reproducing apparatus in which rotary magnetic heads can reliably trace recorded tracks on a magnetic tape by changing a spatial positional relation between a rotary locus plane of the rotary magnetic heads and the magnetic tape in response to a change of running speed of the magnetic tape running along a portion of a peripheral surface of a drum in contact therewith.
2. Description of the Prior Art
A typical example of the magnetic recording/reproducing apparatus which performs a recording/reproducing operation by helically scanning a magnetic tape running at a certain speed along a peripheral surface of a drum composed of an upper drum and a lower drum in contact with a portion of the peripheral surface with rotary magnetic heads (referred to as "magnetic head", hereinafter) may be a video tape recorder (referred to as "VTR", hereinafter).
It is usual that a VTR of this type is provided with, in addition to a function of a normal reproduction in which a recorded information is reproduced while running a magnetic tape at the same speed as that used in recording operation, functions of the so-called variable speed reproduction (referred to as "trick plays", hereinafter) in which a reproduction is performed while running a magnetic tape at a speed (including "stopping") different from the magnetic tape speed used in the recording, in a tape running direction which may be different from the tape running direction in a recording operation.
Further, a VTR is also available in which an event is recorded over a considerably long time while running a magnetic tape intermittently as so called "time-lapse"(intermittent) recording or frame-by-frame recording operation and the magnetic tape thus recorded is reproduced at an industry standard tape speed.
In FIGS. 1 and 2, there is shown an example of a general magnetic tape transporting system in the vicinity of a drum assembly 10 of the VTR.
FIG. 1 is a front view of general magnetic tape transporting system in the vicinity of a drum assembly of the VTR.
FIG. 2 is a plan view of FIG. 1 viewed from an upper side of the drum assembly, wherein a guide roller SGR provided at a supply side of a magnetic tape T and a guide roller TGR provided at a take-up side of the magnetic tape T are omitted for simplicity.
Further, in FIG. 2, a straight line L1 bisects a range of the magnetic tape T wrapped around the drum assembly 10, and a straight line L2 intersects perpendicularly to the straight line L1 at a drum axis 18 of the drum assembly 10. It is noted that a position with respect to a rotational direction around the drum axis 18 may be defined by designating an angle in a counterclockwise direction from a lefthand side of the straight line L2 as marked 0 degree in FIG. 2, which is regarded as a reference angle hereinafter.
In these FIGS. 1 and 2, the magnetic tape T supplied from a supply reel (not shown) is transported along a well known transporting system and then wound on the drum assembly 10 composed of an upper drum 10B and a lower drum 10A over a predetermined angle. The magnetic tape T is oriented oblique with respect to the drum 10 by being guided by a supply side guide roller SGR, a supply side slanted pole 1, a take-up side slanted pole 2 and a take-up side guide roller TGR. After passed through the take-up side guide roller TGR, the magnetic tape T is transported by means of a known tape transport system and taken up on a take-up reel (not shown).
During this transportation, a recorded track pattern (referred to as "tape pattern" or "track pattern", hereinafter) such as shown in FIG. 4 is formed on the magnetic tape T by rotary magnetic heads Ha and Hb mounted on the drum 10.
FIGS. 3(a) and 3(b) show a waveform of FM reproduced signals, respectively.
FIG. 4 illustrates a tape pattern.
FIGS. 5(a) and 5(b) illustrate another tape pattern.
In FIG. 4, a straight line connecting a "starting point" at a lower edge of the magnetic tape T to a point +1 and a number of lines parallel to the straight line are center lines of respective tracks. When the magnetic tape T having such track pattern as shown is reproduced while running it in the same direction as a recording direction at the same speed as a recording speed, the rotary magnetic heads Ha and Hb trace the respective tracks, resulting in a normal reproduction.
However, when the magnetic tape running direction and/or its running speed during a reproducing operation are different from those in the recording operation, a locus of the magnetic heads Ha and Hb on the magnetic tape T becomes such as shown by FF(fast forward), STILL or FB(fast backward) in FIG. 4 since a relative linear speed of the magnetic tape T to the magnetic heads is changed.
In FIG. 4, straight lines connecting the starting point to respective points +2, +3, . . . +7 are loci of the magnetic heads Ha and Hb on the magnetic tape T when the magnetic tape runs in a forward direction, that is, the same direction (shown by a sign "+") as that in the recording operation at a speed twice, triplex, . . . or seven-times the recording magnetic tape speed, respectively (this will be referred to as "FF reproduction", hereinafter).
Similarly, straight lines connecting the starting point to respective points -2, -3, . . . -7 are loci of the magnetic heads Ha and Hb on the magnetic tape T when the magnetic tape runs in an opposite direction (shown by a sign "-") to that in recording operation at a speed twice, triplex, . . . seven-times the recording magnetic tape speed, respectively (this will be referred to as "FB reproduction", hereinafter).
Incidentally, a straight lines connecting the starting point to a point "0" in an upper edge of the magnetic tape T is a locus of the magnetic heads Ha and Hb on the magnetic tape T when a reproducing operation is performed while the magnetic tape T is stopped (this will be referred to as "still repro-duction", hereinafter).
For a VTR of VHS system (an industry standard system) which is a typical example of VTR system, it is general that a magnetic tape T runs while being helically wound on an outer peripheral surfaces of the drum assembly 10 composed of an upper rotary drum 10B having diameter of 62 mm and rotating at 1,800 rpm and a lower stationary drum 10A over an angular range of about 180.degree.. In a recording of a standard mode (referred to as "SP mode", hereinafter), the magnetic tape is transported at a rate of 33.35 mm/second and a locus recorded with the rotary magnetic head having track width of 58 .mu.m on the magnetic tape T forms a video track angle of 5.degree.58'9.9" with respect to a reference edge Te of the magnetic tape T as shown in FIG. 4. In addition to the SP mode, the VTR of VHS system has a triplex mode (tape runs at 1/3 of the standard tape speed to prolong its play time to 3 times standard, and referred to as "EP mode", hereinafter) in which the magnetic tape T is transported at 11.12 mm/second and recorded with a rotary magnetic head having track width of 19 .mu.m. In the EP mode in which the magnetic tape running speed and the track width are one-third those in the SP mode, respectively, a recording time becomes three times that in the SP mode. However, it is more difficult than in the case of the SP mode to exactly trace the respective tracks with the rotary magnetic heads Ha and Hb in the trick plays, due to the narrower track width recorded on the magnetic tape, as will be described later.
In a case where the magnetic tape T is made stationary, a locus of the rotary magnetic head on the magnetic tape T makes an angle of 5.degree.56'7.4" with respect to the reference edge Te of the magnetic tape T. Further, in this case, a straight line connecting the starting point to the point +7 on the upper edge of the magnetic tape T in the SP mode shown in FIG. 4 makes an angle of 6.degree.10'54" with respect to the reference edge Te of the magnetic tape T and the straight line connecting the starting point to the point -7 in the SP mode makes an angle of 5.degree.42'25.7" with respect to the refer-ence edge Te.
As is clear from the track pattern shown in FIG. 4, the track pattern recorded on the magnetic tape T in the SP mode intersects the locus of the rotary magnetic heads Ha and Hb on the magnetic tape T in the trick plays. Therefore, a normal signal level of an FM signal as shown in FIG. 3(a) can not be obtained. Instead of that, a signal level of the FM signal reproduced in the trick play is considerably changed every time when the rotary magnetic heads Ha and Hb intersect the recorded tracks, resulting in an envelope of the FM signal in one vertical scan period as shown in FIG. 3(b), which exhibits a large variation. Due to this fact, an image reproduced in the trick plays contains noise and is low in quality.
Recently, a VTR of new type which is capable of recording/reproducing a High Definition TV (a trade name, referred to as "HDTV", hereinafter) image information has been proposed in which a magnetic tape T is recorded with 3 tracks simultaneously in parallel each being 19 .mu.m wide to form a recorded pattern such as shown in FIG. 5(a). In this VTR, two adjacent tracks of the 3 tracks are used by two rotary magnetic heads whose azimuth angles are opposite each other, to perform a recording/reproducing of a video image signal and the remaining one track is used by another pair of rotary magnetic heads to perform a recording/reproducing of a sound signal.
In a case where a magnetic tape T recorded by the new type VTR is reproduced while feeding or rewinding the tape at a higher speed than a recording speed, a locus of the rotary magnetic heads on the magnetic tape T becomes a straight line connecting a "starting point" in FIG. 5(a) to a point on an upper edge of the tape indicated by +7 or -7, so that the rotary magnetic heads perform the reproducing operation while intersecting many of the "three-times" recorded tracks on the magnetic tape T causing a reproduced image to include noise-bars.
Further, there are many digital VTRs for home use which have been proposed recently, in which an image signal is recorded by compressing an amount of data thereof with using the High Efficiency Coding System. When, in such digital VTR, a rotary magnetic head performs a reproduction such as FF reproduction or FB reproduction in which the rotary magnetic head crosses recorded tracks of a magnetic tape, an image reproduction may become completely impossible dependent on orientation of data blocks arranged in a mosaic.
In order to solve such problem, it is enough to make the locus of the rotary magnetic head coincident with the recorded track of the magnetic tape T. In order to realize this, the following methods have been proposed:
(1) A rotary magnetic head is mounted on an electro-mechanical transducer as an actuator and the rotary magnetic head is displaced to a direction intersecting the recorded track of the tape by controlling the electro-mechanical transducer by means of an open or closed loop control circuit so that the magnetic head follows the recorded track; and PA1 (2) As disclosed in, for example, Japanese Utility Model Publication No. 63-34126 or Japanese Utility Model Laid-open No. 61-158633, a rotary drum on which magnetic heads are mounted and a lower drum are inclined together so that the rotary magnetic heads follow the recorded track of the magnetic tape T.
A description is given to a magnetic tape recording and reproducing apparatus (magnetic recording/reproducing apparatus) disclosed in the Japanese Utility Model Publication No. Sho 61-158633, which is filed by the present Applicant, referring to FIGS. 6 and 7.
FIG. 6 is a perspective view showing a whole construction of a magnetic recording and reproducing apparatus in the prior art.
FIG. 7 is a front view showing a magnetic tape transporting system in the vicinity of the drum assembly.
Referring to FIGS. 6 and 7, this apparatus comprises a drum assembly 10 inclined at an angle .phi. in a direction of an arrow A1, a supply side guide roller SGR and a slant pole 1 each provided at a tape inlet side of the drum assembly 10, a take-up side guide roller TGR and a slant pole 2 both provided at a tape exit side of the drum assembly 10, along a magnetic tape running direction. A magnetic tape T forms a tape path from a supply side reel 3 till a take-up reel 9 by contacting with an erase head 4 and an impedance roller 5 and being wound around the drum assembly 10 over a predetermined range and contacting with the audio control head 6 and being taken up with the take-up reel 9. The magnetic tape T is transformed by being driven and interposed between a pinch roller 8 and a capstan 7.
The drum assembly 10 comprises the lower stationary drum 10A and the upper rotary drum 10B with a magnetic head Ha and Hb. The upper drum 10A is rotated with respect to a drum shaft 18 of a drum motor 19 which is integrally provided on the lower stationary drum 10A. Under the lower stationary drum 10A, a drum support member 11 is fixed. The drum assembly 10 is obliquely provided on a chassis 14 in directions of arrows A1, A2 by causing a pair of pins (one of them is depicted) installed on the drum support member 11 to be pivoted on a pair of protruding holders 14a of the chassis 14.
A reference numeral 15 designates a stepping motor, which is fixed under the chassis 14. A reference numeral 16 designates a steel-belt having stiffness and one end of the steel-belt 16 is fixed at an arm member 11a of an arm 11 and another end thereof are fixed at a pulley 17 provided at a motor shaft 15a of the stepping motor 15, respectively. The drum assembly 10 changes its declined angle by a stepping rotation of the stepping motor 15. The declined angle is securely held at a position which is regulated by a stop position of the stepping motor 15.
An under portion of the lower stationary drum 10A comprises a smaller diameter part 10A-1 and a larger diameter part 10A-2. A reference numeral 12 designates a tape guiding member and it has about a half cylindrical shape, i.e., an arcuate shape. An upper edge of the tape guiding member functions as a lead 12a for guiding or regulating a reference edge Te of the magnetic tape T during tape transportation along the drum assembly 10. The tape guide member 12 is disposed around the lower stationary drum 10A and is fixed on the chassis 14 in such a manner as the pair of protruding holders 14a are accommodated within a cutout 12b of the tape guide member 10.
Thus, upon the FF or FB reproducing operation, it is possible to adjust the locus of the rotary magnetic heads Ha, Hb to the locus recorded on the magnetic tape T by inclining the drum assembly 10 in accordance with the transportation speed of the magnetic tape T.
However, in a VTR which employs the method (1) above, the electro-mechanical transducer must be provided in a small space within the rotary drum and, therefore, the electro-mechanical transducer must be small in size and compact in shape. It is difficult to sufficiently displace the rotary magnetic heads with such small electro-mechanical transducer. Further, it is necessary to maintain a head-touch state of the rotary magnetic heads with respect to the magnetic tape acceptably even if the rotary heads can be displaced considerably by the electro-mechanical transducer. However, it is difficult to always maintain such acceptable head-touch by using a small actuator having an acceptable operational characteristics. In addition, with such actuator, due to its limited frequency-amplitude response, capability of noiseless search is practically limited up to .+-.3 times speed in the SP mode, thus a .+-.5 times or a .+-.7 times speed noiseless search can not be realized.
In a VTR which employs the method (2), particularly, disclosed in Japanese Utility Model Publication No. 63-34126, an arc shaped tape lead for guiding the reference edge Te of the magnetic tape T substantially point-contacts with the reference edge Te. Therefore, a portion of the reference edge Te which does not contact with the tape lead becomes very unstable necessarily. Although the normal reproduction is possible when the magnetic tape T is recorded at relatively low recording density, that is, when the width of recorded track is relatively large, it is impossible to sufficiently remove noise-bars in the FF or FB reproduction. This problem becomes more severe when the magnetic tape T is recorded at relatively high density such as in EP mode operation of a VTR of the VHS system, that is, when the recording track width is relatively small.
On the contrary, in a VTR disclosed in Japanese Utility Model Laid-open No. 61-158633, in which the tape guide member 12 for guiding the reference edge Te of the magnetic tape T over a predetermined distance is provided in a fixed portion of the VTR arranged separately from the lower drum, it is possible to remove the positional deviation of the reference edge Te which may be caused in the magnetic recording/reproducing device disclosed in Japanese Utility Model Publication No. 63-34126, during at least the normal reproducing operation.
However, the VTR disclosed in Japanese Utility Model Laid-open No. 61-158633 has a problem as follows:
Since the tape guide member 12 is provided in a fixed portion of the VTR arranged separately from the lower stationary drum 10A and the upper rotary drum 10B and the lower stationary drum 10A are independently arranged on the chassis 14, respectively, it is very difficult to precisely coincide the center axis of the drum assembly 10 with the center axis of the tape guide drum 10.
Specifically, it is essential to maintain a setting accuracy of the tape guide member 12 to the chassis 14, a setting accuracy of the pair of pins 13 to the drum assembly 10 and a machining accuracy of a pair of holes in the protruding holder for pivoting the pins 13, otherwise, a linearity of the locus recorded on the magnetic tape T by the rotary magnetic heads Ha, Hb will not be obtained.
Further, the tape guide member 12 used herewith is usually made of an aluminum or an aluminum alloy, thus the stiffness of the tape guide member 12 is not strong enough to prevent a distortion from occurring in addition to the arcuate shape thereof.